The approaches described in this section could be pursued, but are not necessarily approaches that have been previously conceived or pursued. Therefore, unless otherwise indicated herein, the approaches described in this section are not prior art to the claims in this application and are not admitted to be prior art by inclusion in this section.
The Stream Control Transmission Protocol (SCTP) is a general-purpose transport layer protocol providing a service similar to TCP (Transmission Control Protocol) plus a set of advanced features to use the enhanced capabilities of modern IP (Internet Protocol) networks and to support increased application requirements. Nowadays, there are SCTP implementations for all major operating systems.
The SCTP protocol, as specified by the IETF, is used in 3GPP (3rd Generation Partnership Project) for transporting signalling information within a cellular core network. SCTP was designed to address certain limitations inherent to TCP for the transport of signalling for telephony over IP. One of the main design goals of SCTP was the efficient transport of small messages in a network fault-tolerant way, important for transporting signalling messages. Thus, SCTP provides a reliable data transmission service for the transport of service messages to applications users.
SCTP is a connection-oriented general-purpose transport protocol that preserves message boundaries. An SCTP connection, called an SCTP association, can be used on top of IPv4 and IPv6.
The messages are encapsulated in data structures called chunks. The chunks are themselves encapsulated in SCTP packets. Moreover, SCTP incorporates several new features that are not available in TCP.
One of the most important enhancements provided by SCTP over traditional transport layer protocols is multihoming. This multihoming feature allows an SCTP association to use several source and destination addresses. Then, each node can be accessed by several addresses set at the establishment of the association. The addresses of transport are exchanged during the initialization of an SCTP association.
The multihoming feature was used up to now as a way to provide reliability. Whenever a primary path between a source and a destination fails, the SCTP association remains as traffic can continue to flow over one of the secondary paths.
Recently it has been proposed to use concurrently the different available connection paths allowed by SCTP in such a way that the overall bandwidth is increased, inherently enhancing mobility management.
Besides the above described default TCP like behaviour, SCTP supports also non acknowledged traffic, UDP (User Datagram Protocol) like, in an extension named SCTP-PR (SCTP-Partial reliability) specified in RFC 3758.
In an article by F. Yong, W. Chee and S. Ramadass, entitled “M-SCTP: transport layer multicasting protocol,” in National Computer Science Postgraduate Colloquium (NaCSPC), 2005, a scheme that utilizes multicast SCTP (M-SCTP) is described. The scheme adds an M-SCTP server stack between an SCTP server and its SCTP clients. The server stack manages the resources of a multicast service and controls multicast membership. However, the scheme achieves multicast capability by using recursive unicast protocol message transmissions. In other words, multicast is realized by the server stack by duplicating data packets and sending them to each client individually using multiple unicast protocol message transmissions. Thus, the scheme does not solve problems stemming from low bandwidth efficiency or poor system scalability.
The document WO2011/071474 evokes the advantages of a scheme allowing the adding of a multicast support to SCTP.
The idea is to operate the SCTP transport protocol in a multicast environment whereas, as explained in the previous paragraphs, SCTP has been primarily designed for unicast TCP/UDP like connections.
There are numerous cases, and in particular when considering video distribution, where it is interesting to beneficiate from multicasting and/or broadcasting. However, it is common to associate with a broadcast medium, a bi-directional medium for robustness, service continuity, etc. Today, it is up to the application to deal with different media and their characteristics such as unicast or multicast.
The prior art, consisting only in multicast over UDP, addresses the case of a source, as a streaming server for example, distributing a stream to multiple destinations over a shared communication link but does not permit concurrent use of multiple links to achieve distribution of such multicast content.
The above cited document WO2011/071474 does not provide the changes to the SCTP protocol to achieve such a multicast transmission.